1. Field of the Invention
This invention relates to a method of preventing vapor explosions caused by contact of two liquids having different temperatures.
2. Description of the Prior Art
The contact and subsequent explosion of two liquids having different temperatures occurs in chemical recovery furnaces when water contacts the pool of molten smelt formed during the recovery of the inorganic cooking chemicals used in the pulping process for wood either by inadvertent introduction of water, water leaks, or introduction of dilute black liquor. The smelt-water system is susceptible to vapor explosions over a range of possible temperatures. A vapor explosion may be defined as a rapid vaporization of an amount of a cooler liquid by heat transfer from a hot liquid. Vapor explosions occur not only in the pulp industry but also, under certain conditions, may occur in the metal smelting, nuclear power and liquefied natural gas industries. The explosion mechanism is not fully understood, although several theoretical mechanisms have been advanced.
Vapor explosions in pulp mills present not only a serious threat to continuous operation of the pulp mill, since some pulp mills utilize only one chemical recovery furnace, but they also pose a continuing threat to the safety of operating personnel at the furnace.
Methods for minimizing or inhibiting such vapor explosions have been advanced, such as by depressing the melting point of the smelt when water encounters the smelt by massive addition of a smelt cooling agent. Sodium bicarbonate, ammonium carbonate and ammonium bicarbonate have been suggested as smelt cooling agents. W. Nelson, "A Theory to Explain Physical Explosions," Tappi, 56, #3, p. 121 (1973); and U.S. Pat. No. 3,615,175. U.S. Pat. No. 3,873,413 teaches the addition of lithium carbonate, lithium hydroxide, sodium hydroxide, potassium carbonate, potassium hydroxide, potassium borate, sodium borate and lithium borate to the pulping cycle in the kraft pulping process to lower the melting point of the smelt to reduce vapor explosions. U.S. Pat. No. 3,447,895 teaches the introduction of an aqueous quenching solution consisting of ammonium sulfate or polymeric glycols onto molten kraft smelt.